Exemplary embodiments relate to a programming method of a non-volatile memory device and, more particularly, to a programming method of a non-volatile memory device, that are capable of reducing the width of a threshold voltage distribution.
A non-volatile memory device that can be electrically programmed and erased and does not require a refresh function of rewriting data at specific intervals may be useful.
An incremental step pulse programming (ISPP) method is a conventional programming method for a non-volatile memory device. More specifically, a program operation is performed while a program start voltage is regularly increased per step voltage.
FIG. 1 is a flowchart illustrating the known programming method of a non-volatile memory device using the ISPP method.
Referring to FIG. 1, a program operation is performed by supplying a program voltage to a word line coupled to memory cells to be programmed at step S11.
A program verify operation is performed to check whether the memory cells have been programmed with a target threshold voltage or higher by verifying the program state of the memory cells using a page buffer coupled to the memory cell block at step S12.
If, as a result of the program verify operation, all the memory cells have been programmed with the target threshold voltage or higher, the verify operation is determined to be a pass, and the program operation is finished. If, as a result of the program verify operation, however, all the memory cells have not been programmed with the target threshold voltage or higher, the verify operation is determined to be a fail. The method continues by setting a new program voltage by raising the program voltage per a step voltage at step S13, and the process returns to step S11.
FIG. 2 shows the threshold voltage distributions of memory cells for illustrating features of the conventional programming method.
Referring to FIG. 2, in the conventional programming method, the memory cells are programmed with a target threshold voltage PV or higher in such a manner that the threshold voltage distribution of the memory cells is raised based on a new program voltage that sequentially rises from a low program start voltage.
As shown in FIG. 2, the right tail A of the threshold voltage distribution is gradually increased according to an increase in the number of program pulses supplied in the ISPP operation. The right tail A is increased because in scaled cell, amount of electron injection during program is statistically varied between cells (Program electron injection spread), then some cells have a large Vt shift by programming pulse.
If, as described above, the right tail A of the threshold voltage distribution is increased Consequently, a multi-level cell (MLC) having a plurality of threshold voltage distributions may malfunction because of a reduced threshold voltage distribution margin.